JPS62244425A - Decomposition of tetranitromethane - Google Patents

Abstract

A process for the management of by-product tetranitromethane (TNM) which avoids the hazards of the prior art isolation or extraction procedures. A selected in-plant liquid or vapour stream, or a reactor off-gas stream from nitration or nitric acid oxidation plant, which contains TNM, is heated to effectively pyrolyse the TNM without undue losses of nitric acid values.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for decomposing tetranitromethane produced when organic substances are treated with nitric acid. In particular, the present invention provides a separate, secondary method for the early separation and economical and continuous destruction of hazardous by-products produced in oxidation or nitration reactions using nitric acid.

The above nitration and oxidation reactions are well known and widely practiced in industry. These processes provide valuable products such as intermediates for manufacturing explosives, pharmaceuticals, dyes, plastics, pesticides, and many other commercial products. However, many of these methods produce large amounts of dangerous by-products, namely tetranitromethane (TNM).
It is not well known that this also occurs.

TNM is dangerous for two reasons. The first reason is its high toxicity. This TNM is rapidly absorbed by the human body through contact with skin debris or inhalation of the vapors. The second reason is TN
Although M is not explosive in its pure state, it easily dissolves hydrocarbons and other non-polar fuels, producing a heavy explosive liquid that is immiscible with water and exhibits great explosive power and high sensitivity. .

The amount of TNM produced as a by-product in other processes is usually very small. However, nitrogen compound-containing fumes
In current methods of recovering and reconcentrating residual nitric acid present in nitrogenic fume and waste acid, the TNM is recycled to the reactor absorbed in the recovered nitric acid. Therefore, even if only small amounts of TNM are produced, the TNM concentration can gradually and cumulatively increase, thus increasing the potential danger.

It is known that the presence of KTNM as an impurity in products is dangerous. The long-term effect of trinitrotoluene has been recognized by the workers at the gunpowder warehouse Jbo. For some nitroglycerin-based explosives,
It has been recorded that the safe storage time is shortened. In order to solve such problems, products have traditionally been washed with a weakly alkaline athrite solution. This process extracts TNM into the wash liquor as the toxic trinitromethane aphrite. However, such treatment PII is not possible for water-soluble products.

TNM is a volatile substance. TNM often escapes from the reactor where it is produced as vapor in the reactor exhaust gas. These gases historically contain nitrous oxides and usually also contain nitric acid vapor. A recovery method for separating such gaseous substances and preventing environmental pollution consists in washing the gas diluted with air with dilute nitric acid.

TNM is not absorbed in this process and is passed through the absorber and released as stack gas. This results in a risk of contamination and a waste of the recoverable nitrogen content in the TNM. Moreover, TNM can also condense as a separate liquid phase under the low temperature conditions in the absorber, thereby creating a distinct danger. Methods have been developed to minimize the release of these TNMs and to extract them from stack gas streams as salable derivatives. U.S. Patent No. 4,001
No. 373 and No. 4,003,977 disclose that TNM is treated with trinitromethide salt by washing the gas stream with an aqueous alkaline solution.
It is described that it is absorbed as 5alt). Next, trinitromethane is liberated by acidifying this waste mine cleaning fluid. This is a dangerous substance that destroys properties very similar to TNM. The disadvantage of the above method is that large amounts of alkali are used and in this case considerable amounts of carbon dioxide are always present in the process gas. Because of these factors and the size and complexity of the equipment required to implement this method, it is believed that this method has not been able to be widely used.

If the chemical reactor is operated at moderate or low temperatures, the by-product TNM may remain dissolved in the waste acid. The recovery operation removes volatile and lipophilic TNM.
is concentrated in high concentrations of nitric acid, which tends to be recycled. U.S. Pat. No. 3,781,374 describes a method for separating TNM from such a nitric acid source. By carefully distilling the nitric acid, it is possible to obtain the most volatile fraction, close to an azeotropic concentrate containing more than 99% of 30 TNM in nitric acid. By separating this fraction, diluting it with water and cooling it, a separate layer of TNM can be obtained below the dilute nitric acid. This TNM
By separating and washing with water, TNM of salable quality is obtained.

The simultaneous dilute nitric acid stream can be reconcentrated and recycled;
These operations require considerable expense.

The economics of this process, the low demand for TNM and the dangers of handling this material in its pure form appear to have inhibited widespread use of the above process.

Therefore, there is a need for a fN convenient method that can completely avoid the toxicity and explosive risks associated with TNM produced as a by-product.

One object of the present invention is therefore a complete and economical process for the decomposition of TNM, a by-product of processes using nitric acid, which eliminates the risks and disadvantages of known processes. The goal is to provide a way to obtain

Another object of the present invention is to provide a method for cold decomposition of TNM without loss of valuable and recoverable nitrogen content. These nitrogen components contain nitrogen oxides inevitably produced by the decomposition of TNM. The simultaneous decomposition of nitric acid also produces minimal amounts of additional nitrogen oxides.

In accordance with the present invention, there is provided a method for selectively decomposing TNM in the presence of other gases, including, inter alia, nitric acid vapor, the method comprising heating a mixture containing TNM at 215 to 300"C.
, preferably 220 to 3006C.

Most preferably it consists of heating to a temperature in the range of 220 to 250'C and holding at this temperature for 0.1 to 100 seconds, preferably 0.5 to 5 seconds. The useful nitrogen content present can then be recovered by cooling and treating the product mixture separately.

It is known that TNM decomposes at some point at elevated temperatures. Surprisingly, however, if an early and economical separation of TNM is carried out, the naturally unstable nitric acid that is necessarily present will not survive the harsh heat treatment to decompose the TNM. It was observed that it remained without decomposing. The economic success of the present invention is primarily based on this surprising finding. This is because it is technically possible to regenerate concentrated oral acid from nitrogen oxides, but it is expensive. The reason for this high cost is that the process requires the use of large equipment for absorption as dilute nitric acid and then the use of significant amounts of energy during reconcentration.

Next, examples of the present invention will be shown.

Example 1 An industrial process for nitrating aromatic compounds to produce plastics intermediates uses nitric acid as the nitration medium. The product mixture exiting the nitration reactor is a solution of plastics intermediates in nitric acid, and this F8 liquid is then sent to a falling film evaporator. In this evaporator most of the nitric acid and TNM are removed upwards as vapor. By condensing this vapor in two stages, 13.5 Kg/hr of TN is produced as a more volatile condensate.
More than 99 H nitric acid containing M (along with dissolved NOx) is obtained at a rate of 2.2 soKq/hr. After treatment in a bleacher to strip most of the dissolved NOx, the stripped condensate stream was sent to a continuous distillation column. 12Kp/
The most volatile top fraction consisting of over 99% nitric acid at 44 Kg/hr containing hr TNM with some residual NO
It was removed as a gas together with x and oxygen. The gas and vapor streams were passed to a pyrolysis device consisting of tantalum tubes without condensation. This tube is heated by an external electrical element and the cass mixture passes through it to 250"CK
Reached. The dimensions of this tube are such that the gas residence time is 1 second. 99% TNM75 in this device
Kf'' was converted to carbon and NOx, and less than 40% of nitric acid was decomposed.

All of this gas mixture was mixed with diluted air and sent to a waste gas recovery tower where nitric acid and NOx (from this unit and elsewhere in the nitration plant) were absorbed into the diluted nitric acid. The concentrated dilute nitric acid from this column was recovered by reconcentration, while the carbon oxide produced by the decomposition of TNM was released into the atmosphere.

Example 2 In an apparatus for producing a herbicide intermediate by nitrating a chemically durable chlorinated aromatic raw material, 100 to 1]5
A mixture of concentrated nitric acid and sulfuric acid at 0.degree. C. is used in a series of reactors. The exhaust gas from this reactor system is a mixture of 60 Kg/br of chlorine and hydrogen chloride, 11% by weight, and 55% carbon dioxide.
, - 1% carbon oxide, 25% nitrate 11112 vapor, 1 tsp water and 5% TNM.

When this gas mixture was placed in a pyrolysis device 11 consisting of an electrically heated quartz tube, the temperature of the gas mixture rose to 250° C. in one second. Through this treatment, more than 99% of T
NM was decomposed, while 99% of nitric acid remained undecomposed. This gas stream is passed through a condenser and then into a gas scrubber using sulfuric acid as the absorption liquid to effectively remove all nitric acid and NOx, and selectively remove remaining chlorine, hydrogen chloride, and carbon dioxide. After treatment in an absorption device, it was released into the atmosphere. The nitric acid and NOx in sulfuric acid are then dissolved and used to produce a new nitrated acid mixture.

It will be apparent to those skilled in the art that TNMO pyrolysis can be carried out at various junctions, but the present invention is practiced at a time when the TNM is at high concentration so that the need for heating and cooling is minimized. is the most advantageous. At the same time, the amount of nitric acid exposed to pyrolysis conditions is minimized.
It is also advantageous to minimize losses due to acid decomposition and regeneration costs. It is also advantageous to arrange for pyrolysis to occur before sending the steam or gas stream to the absorption device.

Claims (1)

[Claims] 1. In a method for decomposing tetranitromethane produced as a by-product in a method of treating an organic substance with nitric acid, a tetranitromethane-containing fraction is heat-treated at a temperature of at least 210°C to decompose tetranitromethane. A method for decomposing tetranitromethane, characterized by: 2. Heat the tetranitromethane-containing fraction to 210 to 300°C.
The method according to claim 1, wherein the method is heated at a temperature of 0.1 to 200 seconds. 3. The method according to claim 1, wherein the method of treatment with nitric acid is nitration. 4. The method according to claim 1, wherein the method of treatment with nitric acid is oxidation. 5. The method according to claim 1, wherein the tetranitromethane-containing fraction consists of exhaust gas and steam. 6. Exhaust gas and steam at a temperature of 220 to 250℃
．． The method according to claim 5, wherein the heating is performed for 5 to 100 seconds. 7. The method according to claim 1, wherein the tetranitromethane-containing fraction comprises nitric acid with a concentration of 68% or more. 8. Add nitric acid to 0.5 to 10% at a temperature of 220 to 250°C.
The method according to claim 7, wherein the heating is performed for 0 seconds.